Means for cooling magnetic cores of electrical apparatus



J. -r. SABOL 2,547,045

MEANS FOR COOLING MAGNETIC CORES OF ELECTRICAL APPARATUS April 3, 1951 2Sheets-Sheet 1 Filed Dec. 4, 1947 Fig. 2 INVENTOR.

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AfTO/PNEK J. 1-. SABOL April 3, 1951 MEANS FOR COOLING MAGNETIC CORES OFELECTRICAL APPARATUS 2 Sheets-Sheet 2 Filed Dec. 4, 1947 INVENTOR. Jon/vSAEDL A TTORNEX Fig; 5

Patented Apr. 3, 1951 MEANS FOR- COOLING MAGNETIC CORES OF ELECTRICALAPPARATUS John T. Sabol, Cleveland, Ohio, assignor to The OhioCrankshaft Company, Cleveland, Ohio Application December 4, 1947, SerialNo. 789,620

6 Claims. (Cl. 175-356) The present invention pertains to electricaltransforming equipment having E-shaped magnetic cores and moreparticularly 'to electrical transforming equipment wherein aconsiderable amount of heat is generated within the center leg of themagnetic core. The invention is particularly-well adapted to anelectrical transformer for high frequencies although it will beappreciated that the invention is not limited to such specific uses.

' Maximum permissible loading of a transformer is limited entirely byits temperature. Sinceit has no moving parts its life depends upon thelife of the insulation, insulation deterioration being a function oftemperature and time. Maximum temperatures usually occur in thelaminations of the center leg of the E and from experience should notexceed 250 F. for continuous operation with conventional core platingmaterials 'and insulation. The temperature of this center leg thusdefinitely limits the maximum loading of the transformer and establishesthe percentage of time during which load can be applied. For instance,with a transformer having a 4" x 4" center le and a 5 turn primary,tests have shown that a duty-cycle ofonly 21% can be maintained when 220volts at 10,000 cycles is applied to the primary, i. e., power can beapplied for 13. seconds during each minute Without exceeding the 250temperature. When 440 volts at 10,000 cycles is applied, the duty-cycledrops to 6% or 4 seconds on and 56 seconds oif." Under such conditions,a large amount of time is thus wasted or a much larger transformer isrequired. Such larger transformer is not only more expensive toconstruct but requires a large amount of space which frequently isdiilicult to provide in many installations where a compact structure isnecessary.

Artificial cooling of this center leg has proven to, be a difficultproblem. Because of the coil windings, circulation of the air over thecenter leg is restricted. No water-cooledlamination was known which,when interleaved with the magnetic laminations, would providesatisfactory cooling and rapidly remove the heat developed.

Accordin ly, the chief object of this invention is to provide atransformer core having new and improved means for cooling itslaminations. A further object is to provide a transformen core havingnovel cooling means which can be readily assembled with the laminations.An additional object is to provide improved means for controlling a rateof flow ofheat into the cooling means of a transformer. A still furtherobject is toprovide improved coolingmeans for a transformer as willpermit the transformer to bereadlly' assembled. Another object is toprovide an l-shaped laminated core of high powerca-rrying capacities forelectro-magnetic apparatu which canbe constructed inexpensively andwhich occupies a greatly reduced space. Yet another object is to providean E-shaped, core-type transformer having an improved duty cycle.

Another object of theinvention. is the provision of a new and improvedcooling lamination for E-shaped transformer cores, the edges of thecenter leg having interconnected cooling tubes associated therewith sothat cooling fluid may be continuously flowed to, along and away-fromthe edges from one end thereof to provide a maximum of cooling therefor.

Other and more specific objects will become apparent upon anunderstanding of the preferred embodiments of the invention describedhereinafter taken in conjunction with the attached drawings which form apart hereof and wherein:

Figure l is a perspective view partly in section of a transformer coreshowing a preferred embodiment of the invention.

Figure 2 is an elevational view partlyin section of a cooling laminationused in the core shown in Figure 1.

Figure 3 is a fragmentary sectional viewon the line 33 of Figure l.

Figure 4 is a view similar to Figure 1 showing a modification of thepreferred embodiment.

Figure 5 is an elevational view of a cooling lamination used in theembodiment shown in Figure 4.

Referring now to the drawings, Figure 1 shows a water cooled transformercore which comprises a main or winding supporting portion A and a keeperor I bar portion B embodying the present invention. The portion A isgenerally E-shaped when viewed from the side, and comprises a pluralityof E-shaped laminations H, each having a base 10, outer legs 12 and I3,and a center leg [4, thelegs extending for an equal distance per.-pendicularly from the base ill in spaced parallel relationship. Thelaminations H are stacked in aligned relationship to a considerablethickness to provide the assembled Winding supportin portion A. Thewinding is normally positioned on the center leg [4. The I or keeper barportion B comprises a plurality of rectangularly shaped laminations I6stacked in aligned relationship to the same thickness as the portion A.The keeper bar B, as shown, is disposed across the ends of the legs l2,l3 and I4 and in abutting relationship therewith. An insulating spacer(not shown) may be provided therebetween if desired. The thickness andthe actual dimensions of the laminations II and IE will depend upon theuse to which the transformer will be put, the, frequency, and the amountof power which it must carry, All'of the design factors are known tothose skilled in theart. The material from which thelaminations II andI6. are made may be of anygrade of magnetic material although-it; hasbeen found sistance to its flow. the cooling plates are made may be asdesired 3? that with the invention a lower grade of magnetic materialmay be employed with equivalent results.

Since high frequency alternations of the flux induce high frequencycurrent in the laminations of all members of the magnetic circuit andbecause of certain unavoidable core losses, these laminations rise intemperature, particularly those in the center leg it, because thewinding assembly prevents any circulation of air over these laminationsand thereby reduces cooling by convection. This rise in temperaturelimits the continuous duty rating of the transformer. In the preferredembodiment selected groups of the iron laminations are replaced bysuitable shaped he'atconducting plates 20 of a metal preferably havinghigher heat conducting qualities than the conventional core materials.

The present invention contemplates a method and means of preventing,controlling or limiting this temperature rise whereby the continuouskva. rating of the transformer may be increased without changing orenlarging the physical dimensions of the core. The cooling plates 2!]are similarly shaped to the laminations H and comprise a base 2 i, outerlegs 22 and 23, and a center leg 24, the legs all extending in spacedparallel relationship fromand perpendicular to the base 2]. The coolingplates 28 are preferably of the identical size to the laminations I I,so that when interleaved with or substituted for some of the laminationsl i, all edges will be flush.

In the embodiment of the invention shown in Figures 1 to 3, a passage 21is formed internally of the periphery of the plate 29, and going fromleft to right, extends across the end and thence down the inner edge ofthe leg 22, across the upper edge of the base 2|, up the left edge,across the end and down the right edge of the center leg 24, across theupper edge of the base 25 and thence up the left edge and across the endof the leg 23. Cooling medium flowing through this passage is thus incontact with a major portion of the periphery of the plate andparticularly on three sides of the center leg 2% where the heatingproblems. of the transformers are most pronounced. The passage 21 may beformed in any desired. manner]. In the preferred embodiment, thesolidportion of the cooling plate 28 has the dimensions, along which thecooling passages are to extend, reduced and a plurality of short lengthsof tubing 26 having a squareouter cross section are, ,then suitablybrazed or otherwise affixed to theseedges as shown. The ends of thetubing befor e .,assembly are mitered so that when in the position shownprovide a continuous internal passage. Ifdesired, a channel or groovecould 'be milled or otherwise cut in the edges of the terial suitablybrazedor soldered in position. The

passages could also be formed internally of the plate 20, i. e., awayfrom the periphery.

The thickness of each cooling plate 28 may be as desired depending uponthe amount of heat which must be dissipated from the internal portion ofthe transformer core. Preferably it should have a thickness as thinaspossible but such that the area of the passage 27 may be sufficient tocarry the cooling medium without excessive re- The material from whichbut are preferably made'from material having high heat conductivity suchas copper or silver.

"Copper would, of'course, be normally used because ofits'lower cost. 3 c

In Figure 1, two cooling plates 20, are shown assembled with thetransformer core. The passages 21 of these laminations maybe connectedin series whereby the cooling medium enters one of the passages, flowsthe length thereof, enters the other passage and flows the lengththereof before being discharged to the drain or otherwise. It is,however, preferred that the passages be connected in parallel as shownto provide a maximum cooling effect for the transformer core andparticularly for the center leg l4. Pipes 32 and 33 are shown providedfor this purpose.

No cooling plates are shown in the keeper bar B although it should beappreciated that if undesirable heating occurs in this member, a coolingplate of similar construction to that shown in Figure 2 but of a shapecorresponding to the shape of laminations "5 could be provided.Alternatively, the legs of the cooling plates 20 could be extended intothe keeper bar as shown in the embodiment of the invention shown inFigure 4.

In the alternative construction shown in Fig ures 4 to 5, like partshave been given like numbers and similar parts have been given the samenumber with a prime mark added. The laminations ll are identical to thelaminationsshown in Figure l and need not be describedfurther. In thepreferred embodiment, the edges of the cooling plates were flush withthe edges of the laminations l I. In this embodiment the base 2| and theouter legs 22, 23 have a width greater than the laminations H and theiredges extend there.- beyond a substantial distance providing elonfgatedlugs 30, 3|, 32 respectively which extend as shown entirely along theouter perimeter of the E-shaped core. Generally the cooling plates inthis embodiment may be of a narrower or thinner construction as noprovision must be made for an internal cooling-medium passage. Also thelegs 22, 23, 24' are lengthened so as to eX- tend upwardly through andbeyond the keeper bar B.

The center leg 2% is provided with laterally extending lugs 34 and 35 ofa length less than the length thereof, providing a space 31 and 38 atthe lower and upper ends respectively of the leg 24, as viewed in Figure5.

As shown when the transformer core is assembled, edges of the coolingplate 20 project outwardly of the edges of the magnetic coresubstantially around the entire edge of the core. The purpose of thelugs is to provide a surface externally of the core to which tubing maybe soldered or brazed. The tubing is to provide a continuous passage ofa cooling medium.

To assemble the transformer core shown in Figure 4, the E-shaped coolingplates ZBfQand the laminations ll are assembled as showuany number ofcooling plates desired being usedfjTh'e electrical windings (not shown)are then assembled on the center leg. An'irregularly shaped tubing 46 ofintegral or built up construction and having preferably a rectangularcross section is then brazed or soldered to the lugs extending beyondthe core. It is to be noted that portions of the length of tubing &6pass through the spaces 31 and'38. The keeper bar 13 is then assembledby sliding the individual laminations in lengthwise or sidewise,=as thevcase may be. .As-in the preferred embodiment, an insulating spacer 48may be provided between the ends of the lamination legs and the keeperbar laminations-l6. In

the embodiment shown, short lengths of tubing are employed, each havingmitered ends which abut and are brazed together when assembled.

b It will be appreciated that the tubing 46 could be formed in onecontinuous length and bent to form the corners.

It will be noted from an examination of the drawings that the sides ofthe tubing adjacent to the edges of the laminations Ii and I B arespaced slightly therefrom. Such a spacing prevents the tubing 46 fromshorting or providing an electrical contact between the individuallaminations H and Hi. It will be appreciated that in normal transformerconstruction the laminations ordinarily have sufficient scale or otherforeign material on their sides to provide a fairly high electricalresistance therebetween which prevents undue leakage currents fromflowing between the individual laininations.

In the preferred embodiment, the cooling plates 20 have dimensionsidentical with the laminations II and the entire transformer core may beassembled in the conventional manner and after assembly suitable wateror other cooling medium connections made to the water passages where itextends laterally from the edge of the core.

It will be appreciated that core clamps or otherwise can be provided tomaintain the laminations in firm side by side or abutting relationship.Such clamps are not shown in the drawmgs.

It has been found for a given size transformer that substituting thecooling laminations shown does not materially affect the operation ofthe transformer even though there is a less amount of iron or magneticmaterial in the core. In fact, because of the cooling ei fect obtained,the power rating of a transformer may be increased by 200% or 300% asthe one factor, that is, internal heating which limited the rating of atransformer before, is no longer a problem. The cooling platesthemselves while being somewhat thicker than the conventionallamination, do not materially interfere with the operation of thetransformer. The electrical resistance of the cooling plates if made ofcopper, is much lower than that of the magnetic laminations and,therefore, the FR loss is much less.

In accordance with the patent statutes, the preferred embodiments of theinvention have been described as a means of illustrating the invention.It will be appreciated that modifications or alterations in thestructures shown will occur to others upon the reading and understandingof this specification. It is my intention to include all suchmodifications and alterations insofar as they come within the scope ofthe appended claims.

Having thus described my invention, I claim:

1. An electrical transformer having an E- shaped core member which tendsto heat when in use, said member comprising a plurality of juxtadisposedmagnetic laminations, each having a plurality of spaced parallel legsincluding an intermediate leg adapted to receive an electrical winding,the space between said legs defining a winding window, means for coolingat least said intermediate leg comprising a plurality of coolinglaminations of relatively high heat conductivity with respect to saidmagnetic laminations interleaved with at least the center leg of saidmagnetic laminations, said cooling laminations including hollow tubesattached to exposed edges thereof adjacent said winding window and meansinterconnecting the ends of said tubes in a continuous manner, whereby acooling fluid may be continuously flowed along said exposed edges tocarry away heat generated in said intermediate leg of said magneticlaminations and conducted to said cooling laminations.

2. The combination of claim 1 wherein said magnetic laminations extendbeyond said cooling laminations at all sides and wherein said tubesextend continuously at least over one exposed edge adjacent said windingwindow across the end and over the other exposed edge adjacent saidwinding window of the center leg of the cooling laminations.

3. The combination of claim 1 wherein the exposed edges of the centerleg of the cooling laminations extend beyond the exposed edges or" thecenter leg of the magnetic laminations and said cooling tubes areattached to said extending portions.

4. The combination of claim 1 wherein the exposed edges of at least thecenter leg of said cooling laminations extend beyond the exposed edgesof the center leg of the magnetic laminations, said extending portionshaving a length less than the length of the center leg or" the magneticlaminations, and said hollow tubes passing through the space formedthereby from one exposed edge of one cooling lamination to anotherexposed edge of another cooling lamination.

5. The combination of claim 1 wherein said core includes a keeper barcomprised of a plurality of juxtadispcsed laminations extending acrossthe ends of said legs and said cooling laminations extend into saidkeeper bar and are interleaved with the magnetic laminations thereof.

5. An electrical transformer having an E- shaped core member which tendsto heat when. in use, said member comprising a plurality ofjuxtadisposed magnetic laminations, each having a plurality of spacedparallel legs including an intermediate leg adapted to receive anelectrical winding, the space etween said legs defining a windingwindow, means for cooling at least said intermediate leg comprising aplurality of cooling laminations of relatively high heat conductivitywith respect to said magnetic laminations interleaved with at least thecenter leg of said magnetic laminations, said cooling laminations havingpassages associated with the exposed edges thereof adjacent said windingwindow and means interconnecting the ends of said passages in acontinuous manner whereby a cooling fluid may be continuously flowedalong said exposed edges to carry away heat generated in saidintermediate leg of said magnetic laminations and conducted to saidcooling laminations.

JOHN T. SABOL.

REFERENCES CETED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 513,420 Rowland Jan. 23, 1894834,148 Lord Oct. 23, 1906 1,331,896 Brand Feb. 24, 1920 1,789,229Gebhard Jan. 1931 1,790,906 Eckman 1- Feb. 3, 1931 1,819,481 PearsonAug. 18, 1931 FOREIGN PATENTS Number Country Date 166,613 Great BritainJuly 28, 1921

